Devils! Not Hallowe’enily cosy at all. Obscenely beguiling, tenebrous creatures of evil, they lurk inside all human nature and they know it. Mother Sawyer’s derisive familiar “Dog” makes that clear, in one of the central couplets of this rural horror-story set in the reeds and fogs of ancient Middlesex:
“Let not the world witches or devils condemn;
They follow us, and then we follow them!”

This finale to the RSC’s “Roaring Girls” season is the oddest of the lot, and by no means the least. Gregory Doran directs the 1621 collaboration between “William Rowley, Thomas Dekker, John Ford&c” (who knows how many spoons in this dark pudding? ) It is a play with two centres, one supernatural and one human melodrama. Mother Sawyer is an impoverished, brutalized old woman regarded locally as a witch (common at the time, not least because of King James I’s obsession with the supernatural). She isn’t one, but in her resentment decides she might as well call up the Devil and serve her persecutors right. It is a marvellous role for an aged woman and Eileen Atkins gives it a brilliant, stroppy, beaky, sardonic presence, with just sufficient pathos to hold sympathy and enough spite to command respect.

The demon she calls up is “Dog” – Jay Simpson near-naked in black body paint, red eyes and a truly horrible tail beneath jagged vertebrae: a starveling rabid cur of a creature who appals and fascinates (worryingly sexy). She sends him to lame horses and ruin the butter of her main foes, but is irritated that he can’t kill the more virtuous.

Because in theology, devils can’t. They work from the inside. So the main tale of the play concerns human misdeeds: seduction, deceit, brutality, hypocrisy, eventually murder. Ian Bonar is the serving-man Frank who has secretly married Winnifride, herself pregnant by her employer. To get a dowry and please his father (Geoffrey Freshwater, all bonhomous bourgeoisie) Frank bigamously marries Susan. His journey from fool to villain is played out with tense, conflicted realism. All the performances are, as you’d expect, fine,: but Faye Castelow as Susan, in her debut RSC season emanates a calm, luminous intelligence, defying the mantra that it is hard to play straightforward goodness. Her scenes with Frank – and her death – are electrifying.

The collision of the two plots, and the local hysteria that “maids who fall” and murderers are being influenced by the Witch, makes it sometimes weirdly and rather excitingly unclear as to what the authors wanted us to believe. This is no CRUCIBLE, because Mother Sawyer does really have a horrid familiar. On the other hand, all her pet Satan can actually do is to upset horses , play tricks and lure poor Cuddy the Morris-man into a bog (nice pondweed on Dafydd Llyr Thomas’ head, I hope he has some good selfies) . Otherwise Dog merely lurks, relishing the natural wickedness of the mortals. Though in a showstopping moment at the end of the longer first act, he takes over the morris-dancers’ fiddle and causes a mass-hysterical diabolic St Vitus’ dance (respect to Paul Englishby’s terrifying score) . What with the skeleton hobbyhorse and the crazed choreography it is definitely one of the must-see sights of this Swan season.

It’s odd, it’s dark, often funny, sometimes touching, and above all it feels like a deep insight into a past moral sensibility: a post-Reformation superstitious unease. The last ten minutes of remorse, forgiveness and wordy justice disengage us, making it retreat into that past again. Unworthily, briefly, you think “Greg Doran could have cut some of that!” . But no. You then reflect that the Royal Shakespeare Company is not just there to give us barnstorming nights out and move us to tears at half the West End prices (both of which it pleasingly often does). It is also there to display, fully and respectfully, our common ancestral past. Demons, moralists and all.